The present invention relates to waterproof roofs, and more particularly to a fastener for securing a flexible waterproof sheet on a supporting roof structure.
Roofs are typically waterproofed by applying segments of sheathing material or sheets which are composed of a waterproof material on the supporting roof structure. These sheets of waterproof material are secured to the supporting roof structure by a plurality of elongated fastening devices which are arranged in spaced relationship along the supporting roof structure. Various types of fastening devices have been utilized in the past, directed to the following U.S. patents which disclose various means for securing sheet material to a supporting structure.
______________________________________ U.S. Pat. No. Inventor ______________________________________ 4,234,799 Eason 3,323,819 Barker 3,574,985 Pierce 3,895,468 Bernstein 4,231,141 Derrick et al 4,246,735 Herzfeld 4,366,656 Simpson 4,502,256 Hahn 4,506,479 Matthison-Hansen 4,519,172 Ristow 4,534,145 Yang et al 4,566,236 Pound 4,586,301 Hickman 4,631,887 Francovitch 4,694,543 Conley ______________________________________
The cited patents illustrate both penetrating and nonpenetrating type of devices for securing sheet material. The Ristow patent is of the penetrating type wherein a fastener actually passes through the sheet member to secure the sheet member in place. In practice, devices that penetrate the sheet member have been found to be undesirable due to the inherent contradication of puncturing a sheet member that is supposed to function as a waterproofing membrane. The Bernstein patent and the Derrick et al patent, for example, illustrate nonpenetrating types of fasteners wherein an overlying clip secures the sheet member to the underlying support structure without penetrating the sheet material.
Fastening devices for securing waterproofing membranes on roofs should also be attached to the underlying support structure in such a manner to provide uniform loading so as to eliminate distortion and permanent deformation of the device by wind uplift forces. Alternate side fastening such as that utilized in the Ristow patent creates uneven loading with varying force moments and levers at severe wind uplift loads to yield permanent distortion and deformation. Further, the manner of fastening the base member to the supporting roof shown, for example, in Ristow may result in screws loosening and backing out which not only endangers the structural integrity of the device but may also puncture the membrane, or may result in the heads of screws actually being stripped out of the base member under severe load conditions. Any of the above conditions may demand product replacement for aesthetic or functional reasons.